Deltaic Faulting and Subsidence: Analog Modeling

LARROQUE, JEAN-MICHEL, Shell Research, Rijswijk, The Netherlands

Scaled experiments with sand layers overlying viscous silicone putty have been used to investigate the behavior of deltaic sediments prograding over salt or mobile shales.

Differential loading caused by a sand wedge prograding over a viscous putty layer induces a forward expulsion of the viscous material. This causes the putty to thin beneath the sand wedge and to thicken at the wedge toe. It results in extension and subsidence in the sand wedge. The predominant dip of the extensional faults is in the progradation direction except in the toe bulge area where a major fault may occur with an opposite (counter regional dip).

The experiments examined how changes in model parameters affect the resultant fault geometries:* Increasing the putty thickness leads to increase in the amount of extension and degree of block rotation, both of which decrease upwards into younger sediments.* A sloping basement/putty interface leads to a significant increase in the extension of the sand wedge.* Fast progradation rates lead to widely spaced faulting whereas slow progradation rates lead to closely spaced faulting.* Basement fault steps, associated with changes in viscous layer thickness, are also demonstrated to locate and locally reorient faults in the overlying sand wedge.* These concepts can assist the interpreter in defining the shape of faulted traps, particularly at depth or where seismic quality deteriorates, and n understanding the evolution and timing of trap formation.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)